1. Field of the Invention
The present invention relates to a recording ink, a method for ink jet recording, a method for producing a color filter, and a color filter, as well as a method for producing a liquid crystal display panel, a liquid crystal display panel, and a yellow ink.
2. Description of the Related Art
Color filters are important components of color liquid crystal displays, and the filters have a structure including a multiplicity of pixels composed of three primary colors, red (R), green (G), and blue (B), arrayed on a transparent substrate.
In recent years, the demand for liquid crystal displays and particularly color liquid crystal displays has increased with the growth of the personal computer market and especially the portable personal computer market. Consequently, strong demands have been made to reduce the cost of liquid crystal displays and particularly expensive color filters, as well as to provide higher-definition-and higher-quality displays, for further growth of the market. These demands are difficult to satisfy simultaneously. Particularly, the former demand on color filters, which occupy a major portion of the cost of products, has been rapidly increased.
Various methods have been attempted in order to achieve cost reductions while satisfying the characteristics required for color filters. No methods satisfying all of the required characteristics, however, have been proposed.
Representative methods for producing color filters will now be described below.
The most popular method is a staining process, in which an easily-stained water soluble polymer material as a staining material and a photosensitizer are applied on a transparent substrate, the coating film is subjected to photolithography to form a given pattern, and the substrate is dipped into a staining bath to form a colored pattern. These procedures are repeated three times to form R, G and B colored layers of a color filter.
The second most popular method is a pigment dispersion process which has taken the place of the staining process, recently. In this process, a photosensitive resin layer containing dispersed pigment is formed on a substrate, and is patterned to form a given pattern in monochrome. The procedures are repeated three times to form R, G and B colored layers of a color filter.
Another method, which is also popular, is an electrodeposition process, in which a transparent electrode pattern is formed on a substrate, and the substrate is dipped into an electrodeposition solution containing a pigment, a resin, and an electrolytic solution to electro-deposit a first color. The procedures are repeated three times to form R, G and B colored layers, followed by baking to yield a color filter.
Protective films are generally formed on the colored layers in each of the first, second, and third methods.
The fourth method is a printing process, which includes dispersing a pigment in a thermosetting resin and printing the dispersion. The procedures are repeated three times to form R, G and B color filter layers and the substrate is heated to cure the thermosetting resin to yield colored layers.
One of common problems of these processes is high production cost due to triplicated coloring or staining procedures that are unavoidable in order to form R, G and B colored layers. Further, such repeated procedures result in a decreased yield.
In the electrodeposition process, the shape of the formable pattern is limited, and thus a color filter prepared by this process is not applicable to thin film transistor (TFT) color liquid crystal displays in the current technology. The printing process is not suitable for fine pitch patterning due to inferior resolution and smoothness.
As described above, several methods are in use for producing color filters. Among them, the staining process using a dye as a coloring material is considered to be the most advantageous from the viewpoint of coloring properties of displays.
However, in the staining process, the substrate is dipped in the staining solution to form pixels, and dyes to which a receiving layer is resistant cannot be employed even though their colors (spectrum characteristics) are satisfactory. As a possible solution to this problem, an attempt has been generally made to introduce a ternary ammonium or other cationic group into the receiving layer when the dye in question is an anionic dye, to thereby improve the dyeing property of the dye. This attempt is intended to increase the number of types of dyes that can be employed. This process, however, invites problems such as variation in the color of the dye (spectrum shift) or decreased heat resistance.
When a staining solution including a plurality of dyes is employed for toning, the dyeing property of an individual dye does not always match that of the receiving layer, and the desired color cannot be reliably obtained. Actually, the color cannot be finely controlled and the types of dyes and materials to be used for the receiving layer are significantly limited.
In order to overcome these problems, methods for manufacturing color filters by means of ink jet systems are proposed in Japanese Patent Laid-Open Nos. 59-75205, 63-235901, 1-217302, and 4-123005. These processes are different from the above-described conventional processes. In these processes, coloring solutions (hereinafter referred to as inks) separately containing coloring matters of R, G and B are jetted out from respective nozzles directly onto a filter substrate, and the inks are dried on the filter substrate to form colored layers (pixels).
These processes require no dyeing process between the dye and the receiving layer as in the staining process, and require no means for improving the dyeing property of the receiving layer such as the introduction of cationic groups. Accordingly, the problems such as variation of color (spectrum shift) of the dye itself prior to and subsequent to dyeing and decreased heat resistance can be avoided. Even when an ink containing a plurality of dyes is employed for toning, the resulting color does not significantly differ from the expected color. According to these processes, the formation of the individual colored pixels of R, G and B can be performed at once, and moreover, less ink is used. Therefore, they have the effects of enhancing productivity to a great extent and reducing the cost.
However, in these conventional methods for producing color filters with an ink jet recording system, the dyes that are used are not always appropriate for the ink jet recording system, and the methods include a lot of uncertainty about matching between the material for the receiving layer and the dye, and the imaging conditions (e.g., the type of receiving layer, and the amount of dye jetted thereon) to be used with the ink jet system. Accordingly, there are the following renewed technical requirements to be satisfied, but no method satisfying all the following requirements has been proposed, and demands are still made for rapid establishment of a method for solving such problems.
(1) The colored portions should have a satisfactory adhesion to the color filter substrate.
(2) The colored portions should have a high color purity (for example, the B pixel should sufficiently shade light in G and R wavelength regions).
(3) The colored portions should exhibit less blurring.
(4) The colored portions should have a satisfactory heat resistance.
Under these circumstances, the present inventors made intensive investigations and found that an ink including an azopyridone dye having a specific structure, in combination with a phthalocyanine dye, can satisfy the above requirements at a high degree as an ink for forming a green pixel of a color filter, and that a yellow ink containing the azopyridone dye having the specific structure is particularly advantageously used as an ink for the formation of yellow images observed through a transmitted light. The present invention has been accomplished based on these findings and further investigations.
Accordingly, it is an object of the present invention to provide an ink which can satisfy the above requirements at a high degree, which requirements are desirable in the production of a color filter with the ink jet system.
It is another object of the present invention to provide a method for ink jet recording using the ink, a color filter having a green pixel formed from the ink, a method for producing the color filter, a liquid crystal display panel using the color filter, and a method for producing the liquid crystal display panel.
A further object of the present invention is to provide a yellow ink which can be advantageously used, for example, in the formation of a yellow image observed through a transmitted light.
The above objects can be achieved by the present invention described below.
Specifically, the present invention provides in one aspect a recording ink comprising at least a water-soluble azopyridone dye represented by the following formula (1), and a water-soluble organic solvent: 
wherein each of A and B is independently a hydrogen atom, a halogen atom, a hydroxyl group, a cyano group, a nitro group, an amino group, a phosphono group, a sulfonyl group, a sulfamide group, a carboxyl group, a trifluoromethyl group, a straight-chain or branched alkyl group, a straight-chain or branched alkoxy group, an aryl group which may have at least one substituent, or a salt of these substances; X is a straight-chain or branched alkyl group, a hydrogen atom, a carboxyl group, or a trifluoromethyl group; Y is a hydrogen atom, a cyano group, a carbamoyl group, a sulfonyl group, a methylsulfonyl group, or a salt of these substances; and Z is a straight-chain or branched alkyl group, and wherein the water-soluble azopyridone dye has at least one sulfonyl group or a salt thereof in its structure.
In another aspect, the present invention provides a method for ink jet recording, which includes the step of performing ink jet recording with the use of the recording ink.
The present invention provides, in a further aspect, a method for producing a color filter, which includes the step of forming a plurality of colored pixels with the use of the recording ink.
In still another aspect, the present invention provides a method for producing a color filter with the use of the recording ink. This method comprises the steps of applying the ink to an ink receiving layer with an ink jet system, which ink receiving layer contains a polymer having an acrylic monomeric unit, and curing the ink receiving layer.
In a still further aspect, the present invention provides a method for producing a color filter, which comprises the steps of applying the recording ink to a substrate; and converting the applied ink on the substrate into a film to thereby form colored pixels, which recording ink further includes a film-forming component and is converted into a film with the application of heat or light or both after the application of the ink.
In another aspect, the present invention provides a color filter which is produced by the aforementioned method for producing a color filter.
The present invention provides, in still another aspect, a color filter containing a green pixel, and the green pixel comprises the water-soluble azopyridone dye represented by formula (1) and a phthalocyanine dye represented by the following formula (2): 
wherein each of R1, R2, R3, and R4 is independently a hydrogen atom, a sulfonyl group, a sulfamide group, a carboxyl group, a halogen atom, a hydroxyl group, a cyano group, a nitro group, an amino group, a phosphono group, a trifluoromethyl group, a straight-chain or branched alkyl group, a straight-chain or branched alkoxy group, an aryl group which may have a substituent, a phenoxy group which may have a substituent, a thiophenoxy group which may have a substituent, a phenyl group which may have a substituent, or a salt of these substances; M represents two hydrogen atoms, two Na atoms, two Li atoms, two metals, or a trivalent or tetravalent metal derivative, and wherein the phthalocyanine dye has at least two sulfonyl groups or salts thereof in its structure.
The present invention further provides a method for producing a liquid crystal display panel with the use of the aforementioned color filter.
In a yet further aspect, the present invention provides a liquid crystal display panel which includes the color filter.
In addition and advantageously, the present invention provides a yellow ink comprising the water-soluble azopyridone dye represented by the formula (1) and a water-soluble organic solvent.
The present invention can easily and economically provide satisfactory color filters.
In addition, the present invention can provide a liquid crystal panel having satisfactory characteristics by, for example, arranging a panel substrate facing the color filter produced by the invented production method, and encapsulating at least a liquid crystal composition into a gap between the filter and the panel substrate.
Further objects, features and advantages of the present invention will become apparent from the following description of the preferred embodiments with reference to the attached drawings.